METHOD OF DETERMINING SERVICE LIFE OF STEEL ARTICLES Russian patent published in 2019 - IPC G01N3/00 

FIELD: defectoscopy.

SUBSTANCE: invention relates to non-destructive testing of materials. Method of determining the service life of steel articles involves measuring the parameters of mechanical properties of the article at different intervals during operation and determining the resource by changing parameters. Note here that steel hardness is measured on steel article tested by non-destructive methods in minimum loaded zone, steel chemical composition is determined, and product operation time is defined till test moment. Standard samples are made from steel with chemical composition identical to that measured in the tested article. These specimens are thermally treated so that to obtain hardness corresponding to that fixed in the tested article. These samples are tested by stretching. Determining the true stresses corresponding to the degree of relative plastic deformation of the sample metal, plotting the graph of the function "true stresses – value of relative plastic deformation to the degree ½" according to the graph of this function, determining the inflection points of the function, degree of relative plastic deformation corresponding to the first inflection point on the graph is determined. Coercive force value in steel at different degree of relative plastic deformation is determined. Value of coercitive force in the sample is fixed corresponding to the degree of relative plastic deformation at the first inflection point. Maximum loaded zone of article is determined, maximum value of coercive force of steel is determined in maximum loaded zone of tested article. Resource P of allowable operation of article is determined from the ratio: P=(H_c^D - H_c^M)/C(H_c), where H_c^D – value of coercitive force in sample, with deformation corresponding to first inflection point on graph of "true stresses – value of relative plastic deformation to degree ½", H_c^M is maximum value of coercitive force in maximum loaded measurement zone on article, C(H_c)=(H_c^M – H_c⁰)/T – rate of change of coercive force in time, T – time of operation of article until test moment, H_c⁰ – value of coercitive force on sample at zero degree of deformation.

EFFECT: invention can be used in nondestructive evaluation of service life of steel products after long service life.

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